Synthesis and characterization of thorium, uranium and cerium oxide nanoparticles

Abstract

Actinide oxides / Nanoparticle / Mesoporous silica / Ultrasound Summary. We describe the synthesis of cerium, thorium and uranium oxide nanoparticles embedded in a mesoporous matrix as template in a kind of nanocasting technique. The solid matrix is used as a template to obtain and stabilize the actinide oxide nanoparticles. We apply high resolution transmission electron microscopy (HR-TEM) to show evidence of metal oxide incorporation into the matrix pores and analyze their structure. Measured interplanar distances and calculated lattice parameters for synthesized nanosized CeO 2−x and ThO 2 samples differ from their bulk crystalline counterparts. We obtain with our synthesis CeO 2−x particles containing both Ce 4+ and larger sized Ce 3+. The lattice parameter for these ceria nanoparticles is found to be larger than the bulk value due to the presence of Ce 3+ with its larger ionic radius. The presence of Ce 3+ was established by means of high resolution X-ray emission spectroscopy (HRXES), applied to the investigation of nanoparticles for the first time. The ThO 2 nanoparticles exhibit a decrease in interplanar distances, as one might generally expected for these nanoclusters. However, the lattice distance decrease for our particles is remarkable, up to 5%, indicating that contact with the surrounding silica matrix may exert a bond distance shortening effect such as through significant external pressure on the particle surface.

Size Dependence of Lattice Parameter and Electronic Structure in CeO2 Nanoparticles

“…Different hypotheses have been put forward to explain this phenomenon: surface stress induced by the presence of sorbed species and partial reduction of Ce IV to Ce III . [9][10][11] Furthermore, the electronic structure and its size-dependence, is of fundamental interest as energetic and catalytic properties notably lie on it. 2 In the present work, the crystal structure of as-synthesized CeO2 NPs was characterized by using…”

Size Effects in Nanocrystalline Thoria

“…To date, the following methods have been proposed for thoria NP preparation: thermal decomposition of thorium salts, − the hydrothermal route, ,, template synthesis, electrochemical deposition, , the sol–gel technique, , and the “heating-up” method . The thermal decomposition method of ThO 2 NPs production is the most widely used.…”

“…Moreover, the chemical precipitation technique is of great interest for environmentally benign science mass production, as it does not require any special conditions or costly equipment. Chemical precipitation of crystalline ThO 2 particles has been reported by several researchers. , In these papers, thermal treatment was used to enable the formation of highly crystalline ThO 2 particles. Batuk et al precipitated ThO 2 in a mesoporous matrix at room temperature and with further thermal treatment at 250 °C in air.…”

Understanding the size effects on the electronic structure of ThO2nanoparticles

“…NPs are of fundamental concern in nuclear material research: they have a primary role in the migration of radionuclides in contaminated sites and nanostructuring the nuclear fuel pellets can potentially improve their mechanical and thermal properties. 24,25 The interest in actinide-based NPs is increasing, [26][27][28][29][30][31] however the size and shape effects on the chemical and physical properties are poorly investigated compared to systems made of lighter and stable elements. The reasons being the safety issues of handling radioactive samples during experiments and the problem of modelling heavy atoms with a partially filled f-shell theoretically.…”